1. Field of the Invention
The present invention relates to a composition which is used as a substitute for hard tissue of a human body (Hereinafter called hard tissue substitute composition.).
2. Description of the Related Art
Compositions comprising a powder ingredient and a liquid ingredient are widely used as a substitute for hard tissue of a human body, and include bone cements, such as a methyl methacrylic-based bone cement, in the medical field, and a root canal filling material or various dental cements, such as cements for bonding, filling, back lining or sealing, in the dental field. These compositions or materials are mainly comprised of a natural or synthetic resin and an inorganic material, and have the drawback of causing adverse effects on living organisms. That is, conventional hard tissue substitute compositions often stimulate organisms and have a poor affinity with an organism due to the heterogeniety of the composition obtained from the material of an organism. Thus, a hard tissue substitute composition without stimulus and pyrexia and having an excellent workability has been sought.
As a material having compatibility with an organism, hydroxy apatite (HAP) and .alpha.-tricalcium phosphate (.alpha.-TCP) are known (Japanese Unexamined Patent Publication (Kokai) Nos. 59-182263, 60-253454 and 61-71060). However, hydroxy apatite can not be hardened even if mixed with an organic acid solution or an aqueous physiological sodium chloride solution, although .alpha.-TCP can be hardened when mixed with an organic acid or with water. However, although a hardened .alpha.-TCP has a sufficient compressive strength, the disintegration rate of the hardened .alpha.-TCP is high, more than 2%, and this is a drawback. The term "disintegration rate" means the rate of the weight reduction of a mass immersed in water at 37.degree. C. for 24 hours (Japanese Industrial Standard (JIS)-T6602).
As a filling agent for filling cavities resulting from periodontitis, a granule of .beta.-TCP and a hardning mixture of .alpha.-TCP and a polyacrylic acid are known. However, the former has poor filling and workability and the latter has a high rate of disintegration.